A vaporized fuel processing apparatus is known in the art, according to which fuel vapor is collected from a fuel tank and collected fuel is supplied into an intake system of an internal combustion engine. For example, as disclosed in Japanese Patent Publication No. 2015-75032, a vaporized fuel processing apparatus has a canister for collecting fuel vapor from a fuel tank and a pressure sensor is provided in the fuel tank for detecting pressure in the fuel tank, wherein a closed inside space of the fuel tank is pressurized by a jet pump which uses fuel flow pumped out by a fuel pump, in order to detect leakage of the fuel vapor of the fuel tank based on a pressure change in the fuel tank after the pressurization of the closed inside space.
However, in the above vaporized fuel processing apparatus, the pressurization by the jet pump is limited to the inside space of the fuel tank, when a connecting pipe for connecting the fuel tank to the canister is blocked up. It is not always possible to surely detect the leakage of the fuel vapor from the canister. In addition, it is not possible in the above vaporized fuel processing apparatus to detect whether the connecting pipe between the fuel tank and the canister is blocked up or not. It is, therefore, uncertain whether the detection for the leakage of the fuel vapor has been done not only for the fuel tank but also for the canister. In other words, detection accuracy for the leakage of the fuel vapor is not so high.